1. Field of the Invention
The present invention relates to an apparatus and method for manufacturing solder balls used for an electrical and/or mechanical-connection between a semiconductor chip and a substrate.
2. Description of the Related Art
Along with the recent development of highly integrated semiconductor technology, consumers prefer miniaturized electronic products. Accordingly, surface mounting technologies (SMT) have been in widespread use. Technologies for minimizing the mounting space of a semiconductor device, such as Ball Grid Array (BGA) or flip chip bonding, are also being widely employed in packaging semiconductor devices. In order to connect such semiconductor devices with printed circuit board (PCB) substrates, solder balls are used. For example, in a BGA package having a plurality of solder ball seating holes on its rear surface, solder balls are seated in the solder ball seating holes for attaching the BGA package onto a PCB and carried to a furnace for connection, during the manufacture of an electronic device. In other words, the drive to pursue highly efficient, miniaturized, lightweight electronic devices, and to add additional functions to such equipment, has resulted in an ongoing drive for a change in the shape or mounting technique. Specifically, preferred mounting techniques have changed from insertion type mounting using wires into SMT in which solder balls are arranged under an integrated circuit to be directly adhered to a substrate. The SMT can reduce the mounting ability, which is currently more than 3 times that of an IC chip size, to 1.2 times the chip size, thereby reducing the area of a PCB required for connection of chips of a constant size to approximately one ninth ({fraction (1/9)}) the chip size. Since solder balls used in SMT are quite small, it is difficult to manufacture the same by an ordinary fabrication technique. It is also difficult to maintain the solder balls at uniform roundness and size. Further, solder ball manufacturing processes are complex and the yield thereof is poor, which makes mass production of solder balls difficult to achieve. Also, the continuously developing microelectronics industry requires that solder balls be more accurately controlled in size.
Conventional techniques for manufacturing solder balls include wire cutting, disc cutting, pulse atomization and the like. According to the wire cutting technique, wires are cut and are subjected to a heating furnace to become a molten solder, that is, a liquid phase solder. The liquid phase solder is turned into spheres by surface tension of liquid, which is cooled to produce solder balls. The wire cutting process is complex, requiring 34 processing steps from preparation of materials to packaging.
According to the disc cutting technique, as shown in FIG. 1, a panel-like solder 101 is punched to make a disc 102 into a constant size and then heated to produce solder balls 103, like in the wire cutting technique. The disc cutting technique requires 19 processing steps, that is, the processing complexity is somewhat improved compared to the wire cutting technique. However, the disc cutting technique still involves many processing steps and considerable complexity. Also, since the size, roundness, diameter and physical properties of products are attached at uniform levels, the productivity is poor, and, in particular, it is quite difficult to comply with the desire for miniaturizing the sizes of solder balls.
According to the pulse atomization method, as shown in FIG. 2, a molten solder is disturbed by means of a vibrator 202 in a melting furnace 201 to make a molten solder paste supplied from a nozzle 203 into spheres using turbulence. However, according to the pulse atomization method, a vibrating plate 202=a may experience non-uniform vibration due to a distribution in the temperature of the molten solder throughout the melting furnace 201, a Marangoni effect in the melting furnace 201 or natural convection. Accordingly, the solder balls produced are not uniform in size, resulting in deterioration of quality. In order to obtain uniform sized solder balls rather than different sized solder balls, multiple steps of size assortment must be performed, which degrades the productivity and yield.
To solve the above-described problems, it is an object of the present invention to provide an apparatus and method for continuously manufacturing smaller solder balls in uniform sizes.
To accomplish the above object; there is provided an apparatus for manufacturing solder balls, the apparatus including a melting furnace having a nozzle through which a molten solder paste flows and drops, for producing solder balls; a vibrating means attached to the nozzle of the melting furnace, for applying vibration to the nozzle; and a vibration controlling means for controlling the vibration frequency of the vibrating means to adjust the size of the solder balls dropped from the nozzle.
According to another aspect of the present invention, there is provided a method for manufacturing solder balls, the method including the steps of setting a vibration frequency according to a desired solder ball size, applying vibration to a nozzle with the set vibration frequency, making the molten solder paste flow through the nozzle to manufacture solder balls of a predetermined size according to the vibration frequency, and measuring the size of the manufactured solder balls. Since the solder balls are manufactured using nozzle vibration, the accuracy, roundness and recovery efficiency of the solder balls are excellent. Also, the apparatus and method for manufacturing solder balls can be simplified, thereby increasing the productivity.